DENITRIFICATION FROM SOILS OF A YEAR-ROUND FORAGE PRODUCTION SYSTEM FERTILIZED WITH LIQUID DAIRY MANURE

Denitrification Is an important potential sink fur N in liquid manure and the amount of denitrification may affect sustainability of crops g rown,vith liquid manure as a nutrient source. This study examined gase ous N loss by denitrification and the changes in soil N pools after li quid manure application, Liquid dairy manure was applied at four N rat es (246, 427, 643, and 802 kg N ha(-1) yr(-1)) to four quadrants of a center-pivot in a gear-round forage production system, Denitrification (using the acetylene block technique on intact cores) and soil N pool s were determined before and for 2 yr after beginning liquid manure ap plication. Nitrous oxide evolution from soil cores was compared to den itrification for a third year of the study. Denitrification rates and soil N pools increased after manure application at all rates of applic ation. The two highest rates of manure had highest denitrification rat es, although differences in soil moisture due to soil and drainage pro perties complicated the interpretation of manure rate effects. At the two highest rates of N application and two lowest rates of N applicati on, the quadrant with higher soil moisture had higher denitrification, Nitrous oxide emissions accounted for about 29% of total denitrificat ion, Denitrification ranged from 11 to 37% of total N applied in the m anure. highest rates of denitrification and highest proportions of fet al N denitrified were found with the second highest manure application rate because these soils were wetter, Annual denitrification totals r anged from 32 to 114% of the excess N (application-crop uptake) availa ble.